1. Field of the Invention
The present invention relates to a ball-balancing robot, and in particular to a ball-balancing robot capable of maintaining a predetermined posture while balancing when rotating about a vertical axis.
2. Description of the Related Art
Examples of a ball-balancing robot include a robot that is configured to be able to maintain a predetermined posture while balancing on a single spherical object, and this type of a robot is configured to be able to move by rolling the spherical object and to rotate about a vertical axis that passes a center of the spherical object.
Further, as one example of such a ball-balancing robot, Japanese Patent Application Laid-Open No. 2005-342818 discloses a ball-balancing robot 101 as illustrated in FIG. 5.
The ball-balancing robot 101 disclosed in Japanese Patent Application Laid-Open No. 2005-342818 includes a spherical object 110, and a robot main body 120 provided on the spherical object 110.
The robot main body 120 includes a plurality of drive mechanisms 121 for rolling the spherical object 110, and a posture-controlling actuator 124 for controlling a posture of the robot main body 120. Further, a posture-detection sensor 126 to detect the posture of the robot main body 120 is provided within the robot main body.
Moreover, the robot main body 120 on the spherical object 110 is configured to be able to move to a desired position along with the spherical object 110 by rolling the spherical object 110 by driving the plurality of drive mechanisms 121.
The ball-balancing robot 101 is also configured to allow posture control by moving a weight arranged in an upper part of the robot main body 120 in a horizontal direction to change a gravity center using the posture-controlling actuator 124, and by inclining the ball-balancing robot 101 to a predetermined direction.
In the meantime, in the ball-balancing robot, the robot main body is basically configured such that its gravity center is positioned on a vertical axis that passes the center of the spherical object. As the robot main body is placed on the spherical object, the robot main body may move along with the spherical object and rotate on the spherical object without falling or dropping.
On the other hand, as the robot main body is provided with ornamental elements, a posture-detection sensor, a battery, a control device, and the like, it is difficult to position the gravity center of the robot main body on its axial line in designing the robot.
Therefore, when the robot main body is placed on the spherical object such that its gravity center is positioned on the vertical axis, it is inevitable as it stands that a position and an orientation of the posture-detection sensor provided for the robot main body are somewhat displaced from a designed position and a designed orientation (e.g., a position and an orientation that are rotationally symmetric taking an axial line of the robot main body as a rotational axis).
Further, there is a problem that it is difficult to accurately control the posture of the robot main body, because when the robot main body is rotated about the vertical axis at which the gravity center of the robot main body is positioned and that passes the center of the spherical object (rotate in a yaw direction) in a state in which the position and the orientation of the posture-detection sensor are displaced from an intended position and an intended orientation, the posture-detection sensor detects a component in a different direction generated due to rotation in a yaw direction (e.g., a component in a roll direction) and fails to detect an accurate posture.